Instrumentation for preparing a distal femur

ABSTRACT

A method and apparatus for preparing a planar surface on the distal femur prior to implantation of a femoral knee prosthesis has a femoral plate with an opening therein for exposing both condyles of the femur. A guide with a central aperture is used to align the femoral plate on the distal femur. The guide is releasably secured to the femoral plate and an intramedullary guide rod is placed through the aperture therein and into the intramedullary canal of the femur. After alignment with the intramedullary canal, the femoral plate is pinned to the femur and the rod and guide are removed. A milling guide having two bores, one adjacent each condyle, is then placed on the femoral plate and an end mill is used to mill a planar surface on at least one of the condyles.

This application is a continuation of U.S. application Ser. No.07/920,081, filed Jul. 27, 1992, now U.S. Pat. No. 5,417,695.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for preparing a distalsurface of a human femur. More particularly, it relates to a set ofinstruments and a method for their use to prepare the surface of thefemur to receive a distal femoral prosthesis.

2. Description of the Prior Art

Various types of instruments and methods have been developed to enable asurgeon to affix a distal femoral knee prosthesis to a human femur.Since the purpose for affixing such a prosthesis is to restore thepatient's ability to walk after disease or other traumatic causes haveimpaired that ability, it is important that the prosthesis be attachedto the femur in a manner that will approximate as closely as possiblethe natural condyles which the prosthesis is replacing.

It is a common practice to use the long central axis of the femur as aguide in determining the manner in which the distal femoral surfacesshould be shaped to receive a properly aligned distal femoralprosthesis. Using the long central axis of the femur as a guide, aplanar distal cut is first made on the distal femur and then the guideis removed and additional instrumentation utilizes the planar distalsurface as a reference from which to cut anterior and posterior cuts,followed by anterior and posterior chamfer cuts.

Patents showing such a method or methods similar thereto are U.S. Pat.Nos. 4,474,177 and 4,721,104. The former patent relates to a series ofinstruments for preparing the distal femur in which an angled alignmentguide is used to index a plateau planar which is used to prepare theplanar distal surface of the femur. The latter patent relates to asurgical apparatus for preparing the intracondylar area of the distalfemur.

U.S. Pat. No. 5,047,032 relates to a surgical instrument designed toproduce a planar distal femoral surface. A router or side cutting drillis used to form the surface. Another patent which relates to thepreparation of the distal femur is U.S. Pat. No. 4,787,383, in which asaw is used to make the planar femoral cut. A saw guide is alsodisclosed.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an apparatus for formingplanar surfaces on the medial and lateral condyles of the distal femurwhich is simple in design.

It is another object of the invention to provide a method for using theapparatus which method is simple to perform and therefore saves timeduring surgery.

These and other objects are achieved by an apparatus for milling aplanar distal femoral surface which surface contains at least one of themedial and lateral condyles of a femur. The apparatus is initiallylocated by use of an intramedullary rod extending into theintramedullary canal of the femur. The guide rod aligns a guide blockwhich in turn aligns a ring-like femoral plate having a generally oblongopening therein which exposes both the medial and distal condyles whenthe plate is secured to the femur. The plate is secured to the medialand lateral surfaces of the distal lemur by drill pins. The femoralbushing guide block fits within the generally oblong opening in thefemoral plate and has a central hole therein angled laterally at anangle of about 8° from a direction perpendicular to the face of thefemoral plate. Once the femoral plate is aligned, the guide block,bushing and rod are removed and a milling guide block having a pair ofcylindrical medial and lateral guide bores therein adjacent therespective medial and lateral condyles is placed thereon. The millingguide block is inserted into the oblong opening in the femoral plateafter the femoral plate is firmly secured to the femur and the femoralbushing and guide block which hold the intra-medullary rod is removedtherefrom. The distal milling guide has a generally oblong shape whichis snugly received within the oblong opening in the femoral plate. Acylindrical end mill cutter is inserted in at least one of the medialand lateral bores for milling said medial or lateral condyles. The endmill cutter has a bottom surface with at least two blades aligned to cuta flat surface. The milling of only one condyle would be required in auni-condylar knee replacement wherein a prosthesis is implanted only onone of the condyles.

The milling guide block has a circumferential rim thereon for engaging aflange on the distal end mill cutter to permit milling of the condylesto a predetermined depth. This depth can be varied by placing aring-like spacer between the flange on the distal end mill cutter andthe rim on the milling guide block which surrounds the opening in themilling guide block.

These and other objects and advantages of the present invention willbecome apparent from the following description of the accompanyingdrawings, which discloses one embodiment of the invention. It is to beunderstood that the drawings are to be used for the purposes ofillustration only and not as a definition of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, wherein similar reference characters denote similarelements throughout the several views:

FIG. 1 is an exploded isometric view of the distal femoral plate of thepresent invention including the bushing block and bushing for thealignment thereof;

FIG. 2 is an elevation view showing the distal femoral plate of FIG. 1in alignment on and connected to the distal femur;

FIG. 3 is an exploded isometric view of the end mill and milling guideof the present invention prior to being inserted into the distal femoralplate;

FIG. 4 is an elevation view of the end mill of FIG. 3;

FIG. 5 is a bottom view of the cutting surface of the end mill of FIG.4; and

FIG. 6 is an elevation view of the distal femoral plate mounted on afemur with the components of FIG. 3 located therein.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 there is shown a distal femoral plate 10 which, inthe preferred embodiment, is in the form of an oval ring-shaped body 12having a longitudinal axis 14. Body 12 has a top surface 15, a bottomsurface 17 and an inner surface in the form of wall 13. Body 12 has apair of flanges 16 at each end thereof which flanges are centered withrespect to longitudinal axis 14 and, in the preferred embodiment,coupled to body 12 by screws 18.

As seen in FIG. 2, the length of ring-shaped body 12 along longitudinalaxis 14 in the preferred embodiment is selected to accommodate both themedial and lateral condyles 62, 64 of the distal femur 60. Thus, thedistance between flanges 16 along axis 14 is sufficient so that thebottom surface 20 of each flange 16 extends proximally beyond the distalsurface of the distal condyles. A pair of pin holes 22 are formed inflange 16 and are adapted to receive pins 66 which will be discussed ingreater detail below. In the preferred embodiment holes 22 are angledinwardly toward the proximal end of femur 60. An axis 38 extending in adirection perpendicular to a plane containing top surface 15 of body 12is located along axis 14 intermediate flanges 16.

Again referring to FIGS. 1 and 2, there is shown a femoral bushing guideblock 24 having a flange 27 forming a stop surface thereon. A generallyoblong wall 26 extends proximally from stop surface 27 of block 24. Wall26 is shaped to be slidably received within interior surface 13 of ring12. The lower surface of flange 27 engages top surface 15 of femoralplate 10 to limit the penetration of the guide block 24 therein. Femoralbushing guide block 24 also includes a central bore 28 coaxial with axis38 and sized to receive cylindrical end 30 of an intramedullary rodbushing 32. Bushing 32 includes a bore 34 for receiving anintramedullary guide rod 40. Bore 34 in intramedullary rod bushing 32extends along the longitudinal axis 36 which is angularly offset frombore 28 within femoral bushing guide block 26. In the preferredembodiment this offset is 5°, 7° or 9°.

In the preferred embodiment, intramedullary rod bushing 32 is madeseparate from femoral bushing guide blocks so that the angle betweenaxis 36 and 38 may be varied, from 5° to 9° by a series of bushings 32,each having an axis 36 varying in 1° or 2° increments with respect toaxis 38.

Referring to FIG. 3 there is shown a distal milling block 44 and femoraldistal plate 10 as previously described. Milling guide 44 is designed tocooperate with the distal femoral plate 10 in a manner similar tobushing guide block 24. Surface 13 of ring 12 of plate 10 receives aproximally extending wall 42 of distal milling guide 44. Similar toguide block 24, milling guide 44 has a stop surface 41 which engagessurface 15 of femoral plate 10. Distal milling guide 44 includes a pairof bores 46 and 48 respectively, which have longitudinal axes 51, 53which are parallel with axis 38. In the preferred embodiment, the axes51, 53 of bores 46 and 48 are offset with respect to a plane containingthe axis 14 of distal femoral plate 10. The reason for this offset willbe described in more detail below. The diameter of both bores 46 and 48is sized to receive a distal end mill cutter 50 shown in FIGS. 3 and 4.End mill cutter 50 includes a milling surface 52 and a drive shaft 54adapted to be connected to a suitable rotating power source. Wheninserted in either bore 46 or 48, the axis of drive shaft 54 is alignedwith axes 51, 53. Spacers 80 may be provided to adjust the depth thatsurface 52 extends beyond the bottom surface 43 of wall 42 of guide 44(i.e. to space flange 55 from surface 47 of guide 44).

Referring to FIGS. 4 and 5, it can be seen that surface 52 containspreferably three blades 58 for end milling a planar surface on thecondyles of the distal femur. Two blades 58 or blades in excess of threemay also be used.

Referring to FIG, 6 there is shown the femoral plate of the presentinvention mounted on a distal femur 60 with mill cutter 50 in its finalposition. FIG. 6 shows distal femur 60 including condyles 62 and 64 withfemoral plate 10 held thereon by four pins 66. Spacer 80 is shown inplace on surface 47 of guide 44, which spacer 80 in the preferredembodiment, is one millimeter thick. One or more spacers may be used toadjust the depth of the condylar planar cut made by end mill 50.

The method of preparing a distal femoral surface by milling the mediallateral condyles 62, 64 of a femur 60 with the apparatus of the presentinvention will now be described. First a femoral bushing guide block 24with an appropriately angled guide bushing 32 mounted in bore 28 thereofis placed into the distal femoral plate 10 with wall 26 slidablyreceived with surface 13 of body 12. In the preferred embodiment a thumbscrew 70 may be used to lock guide block 24 into femoral plate 10. Inaddition, the angular offset between axis 36 and 38 may be any anglebetween 5° and 9° with a series of bushings 32 being provided whichresult in an angular offset of 5°, 7° or 9°.

After bushing 32, bushing guide block 24 and distal femoral plate 10 areassembled, intramedullary rod 40 is passed through bore 34 of the guidebushing 32 and into the medullary canal 76 of the femur 60. The assemblyof distal femoral plate 10, guide bushing 24 and guide 32 are advanceddistally on the rod 40 until contact is made with the prominent condyle62, 64. Distal femoral plate 10 is then rotated so that a posterior wall72 of surface 13 of plate 10 is parallel to a plane containing theposterior surface of the femoral condyles 62 and 64. Drill pins 66 arethen placed through all four holes 22 of flange 16 and into themedial-lateral sides of the condyles. In the preferred embodiment, holes22 are angled toward the proximal end of femur 60 so that the pins 66contact the medial and lateral sides of the condyles away from thedistal area where the milling is t0 take place.

Once the femoral plate 10 is fixed in position by pins 66, the femoralbushing guide block 24, intramedullary rod guide bushing 32 andintramedullary rod 40 are removed. At this point in the surgery, thedistal milling guide 44 is placed into the distal femoral plate andlocked therein with the anteriorly positioned thumb screw 70. Distal endmill 50 is then inserted into circular bore 46 or 48 of milling guide44. End mill 50 includes a flange 55 which contacts surface 47 ofmilling guide 44 and determines the depth of penetration of cuttingsurface 52 into the condyles 62 or 64. In the preferred embodiment, themilling guide penetrates the condyle distally 10 mm, at which timeflange 55 contacts surface 47, thereby limiting penetration. Cylindricalspacer 80 may be used to limit the depth of penetration. For example, a1 mm thick spacer 80 would limit the penetration of surface 52 into thecondyles to 9 mm when it is inserted between flange 55 and surface 47 ofguide 44.

The circular holes 46 and 48 are off center with respect to a planecontaining a longitudinal axis 14 and perpendicular to the plane definedby the surfaces 15 of femoral plate 10 (i.e. they are offset in theanterior-posterior direction with respect to a medial-lateral planethrough the femur). This allows the surgeon to flip the milling guide180° about axis 38 and the longitudinal axis of the femur and milladditional bone in the anterior-posterior plane if necessary to preparea larger planar surface on the distal femoral condyles. Because thecircular bores 46 and 48 are offset in the anterior-posterior direction,a generally oval cut can be made on the condyles.

With the use of the system described above, extremely accurate flat bonecuts are made on both condyles 62 and 64. As with most kneeinstrumentation systems and surgical methods used for the preparation ofthe distal femur for implantation of a prosthetic femoral kneecomponent, all other bone cuts are indexed off this first distal planarsurface on the femur. It is contemplated that these other cuts are madein any well known manner after using the instrumentation of the presentinvention.

While one example of the present invention has been described, it isobvious that many changes and modifications may be made thereunto,without departing from the spirit and scope of the invention.

I claim:
 1. An apparatus for milling a distal femoral surface containingthe medial and lateral condyles of a femur having an intramedullarycanal, said apparatus comprising:an alignment element for connection tothe distal end of the femur, said alignment element exposing at leastone of the condyles when said alignment element is secured to saiddistal femur; means for aligning said alignment element with respect tothe intramedullary canal; means for securing said alignment element tosaid distal femur after being aligned; a milling guide block coupled tosaid alignment element, said guide block having an outer surfaceengaging a positioning means on said alignment element and having atleast one guide therein adjacent a respective medial and lateralcondyles, said milling guide block having a stop surface thereon; and acylindrical end mill cutter for insertion in and sliding engagement withsaid at least one medial and lateral guide in said guide block formilling said medial or lateral condyles, said end mill having a radiallyextending guide surface for engaging said stop surface on said guideblock to permit milling of said condyles to a predetermined depth.
 2. Anapparatus for milling a distal femur as set forth in claim 1 furthercomprising at least one spacer for insertion between said guide surfaceon said end mill and said stop surface on said milling guide block tovary the predetermined depth of said milling of said condyles.
 3. Anapparatus for milling a distal femoral surface containing the medial andlateral condyles of a femur having an intramedullary canal, saidapparatus comprising;a femoral alignment plate for connection to thedistal end of the femur, said alignment plate exposing at least one ofthe condyles when said plate is secured to said distal femur; anintramedullary rod and alignment guide for aligning said femoralalignment plate with respect to the intramedullary canal of the femur;bone pins for securing said femoral alignment plate to said distal femurafter being aligned; a milling guide block coupled to said femoralalignment plate, said guide block having an outer surface engaging apositioning surface on said femoral alignment plate and having at leastone guide therein adjacent a respective medial and lateral condyle, saidmilling guide block having a stop surface thereon; and a cylindrical endmill cutter for insertion in and sliding engagement with said at leastone guide in said guide block adjacent a respective medial and lateralcondyle for milling said medial or lateral condyles, said end millhaving a radially extending guide surface for engaging said stop surfaceon said guide block to permit milling of said condyles to apredetermined depth.
 4. An apparatus for milling a distal femur as setforth in claim 3 further comprising at least one spacer for insertionbetween said guide surface on said end mill and said stop surface onsaid milling guide block to vary the predetermined depth of said millingof said condyles.